The present invention relates to methods of diagnosing faults in internal combustion engines, and more particularly to a snap acceleration test for diagnosing faults in individual cylinders of an engine during operation of the engine under loaded conditions.
One known method of testing internal combustion engines involves the taking of incremental rotational rate data while the engine is being rapidly accelerated from a relatively low speed to a relatively high speed. The patent to Hanson, U.S. Pat. No. 3,994,160 relates to a method employing such an acceleration burst test in order to provide an indication of the overall power of the engine. In the co-pending, commonly assigned patent application of Buck et al, Ser. No. 781,313, filed Mar. 25, 1977, now U.S. Pat. No. 4,295,363, and entitled "Apparatus for Diagnosing Faults in Individual Cylinders in an Internal Combustion Engine", a snap acceleration test is described wherein the data taken is utilized to diagnose faults in the individual cylinders in the engine. In the Buck et al. application, the data consists of a plurality of incremental time interval measurements, each measuring the amount of time required for the engine to rotate through a corresponding small angular increment, taken while the engine is accelerating. Because of the power contributions of the individual cylinders in the engine, these time interval measurements will have generally undulating values. In the Buck et al. application faults in the individual cylinders were determined by comparing the magnitude of these undulations of the individual cylinders, these magnitude values having first been normalized in accordance with the changing speed of the engine.
Although this prior snap acceleration test could successfully diagnose faults, the absolute magnitudes of the various measurements varied substantially as the tests were repeated. This had a tendency to reduce the credibility of the test to the user, even though the fault indications were, in fact, accurate.